         (round-double (area (NACA-design 3 40 12)))) ;; assymetric -- thin foil
 (expect 0.1367
         (round-double (area (NACA-design 9.5 0 20)))) ;; assymetric -- thick foil
+


(expect 0.5165
        (round-double (lower-surface-x-function (NACA-design 9.5 9 40) 0.5)))

;;;-------- riemann-sum ----------
(expect 0.0681

  (:require [expectations :refer :all]
            [hydrofoil.model :refer :all]
            [hydrofoil.core :refer :all]
            [hydrofoil.evolution :refer :all]
            [hydrofoil.utils :refer :all]))

;;; --------- thickness-function tests ------------
; thickness 0:
